Interconnect structures of integrated circuits and semiconductor devices are typically fabricated by forming a series of dielectric layers and conductive layers in order to create a three dimensional network of conductive layers separated by dielectric material. The interconnect structure may be fabricated using, for example, a damascene structure in which a dielectric layer such as a low k dielectric layer is formed atop one or more conductive plugs or sub-layers. In order to form an electrical connection to the conductive sub-layers, the dielectric is patterned and etched to define via openings in the dielectric layer. Formation of the via openings within the dielectric layer exposes a portion of the conductive line. Therefore, reliable formation of these interconnect features is an important factor in ensuring the quality, performance and reliability of devices formed on individual substrates and in each die.
A typical method for forming layers for such interconnection structures includes physical vapor deposition of a barrier layer over a feature, such as a trench or a via, followed by a physical vapor deposition of a metal layer on the barrier layer to fill the feature. One common material often utilized to fabricate the barrier layer is titanium. However, the inventors have observed that achieving the desired coverage of the barrier layer material on the bottom surfaces of the substrate features is increasingly difficult in processes involving smaller features and high aspect ratios (e.g., a ratio of height to width of the feature). For example, the inventors have observed that conventional titanium physical vapor deposition techniques that utilize process conditions bombard the substrate with the deposition material to try to achieve a desired bottom coverage may lead to damage of underlying dielectric layers due to the intensity of the bombardment. This may lead to yield loss, deterioration in reliability and device failure.
Thus, the inventors have provided improved methods for processing semiconductor substrates.